Optimizing Evanescent Efficiency of Chalcogenide Tapered Fiber

Evanescent wave absorption-based mid-infrared chalcogenide fiber sensors have prominent advantages in multicomponent liquid and gas detection. In this work, a new approach of tapered-fiber geometry optimization was proposed, and the evanescent efficiency was also theoretically calculated to evaluate sensing performance. The influence of fiber geometry (waist radius (R_w), taper length (L_t), waist deformation) on the mode distribution, light transmittance (T), evanescent proportion (T_O) and evanescent efficiency (τ) is discussed. Remarkably, the calculated results show that the evanescent efficiency can be over 10% via optimizing the waist radius and taper length. Generally, a better sensing performance based on tapered fiber can be achieved if the proportion of the LP₁₁-like mode becomes higher or R_w becomes smaller. Furthermore, the radius of the waist boundary (R_L) was introduced to analyze the waist deformation. Mode proportion is almost unchanged as the R_L increases, while τ is halved. In addition, the larger the micro taper is, the easier the taper process is. Herein, a longer waist can be obtained, resulting in larger sensing area which increases sensitivity greatly.